There is a strong trend on the part of the electronics industry to increase the density of electronic packaging on printed circuit boards and in semiconductors in order to boost performance and reduce cost. For example, with the increased density of the circuity at the chip level, the number of input/output (I/O) address lines is increased, and this improves communication with other logic circuitry. One problem associated with increasing the number of pins on a semiconductor package is the need to maintain or reduce the assembly cost. As a result, surface mounts or small outline packages have been developed. Without a method to remove the heat from these electronic packages, however, their performance is restricted, as the packages themselves do not contain means by which heat can be conducted away. Moreover, these packages do not incorporate the means by which a heat sink may be attached, and the high density of electronic trace leads emanating from the surface mount package severely restricts the type of attachment method for any heat sink which could be used. This is particularly important as any attachment used to affix heat sinks to these surface mount packages requires that the leads of the package remain accessible after the surface mount package has been attached to the printed circuit board. Also, any proposed heat sink attachment must minimize the stress load on and not damage the delicate leads of the surface mount package. If the leads are damaged by external forces such as might occur in attaching or removing a heat sink, the electrical connections between the surface mount package and the circuit traces on the printed circuit board may be broken.
In the prior art, heat sinks have been attached to such packages by bonding the heat sink to the package with a thermally conductive epoxy that closely matches the coefficient of thermal expansion of the plastic package. There are several disadvantages to this method. First, the application of the epoxy adhesives are labor intensive operations requiring proper mixing and the use of special tooling to attach the heat sink to the package. Further, these adhesives are somewhat hazardous, creating a disposal problem. Once applied, the heat sink cannot be easily removed from the package in the event the package has to be replaced or repaired.